A plasmonic device comprising an odd number of at least three input waveguides and at least one output waveguide is disclosed. In one aspect, the waveguides are adapted for guiding a surface plasmon polariton wave and the input waveguides are connected to the output waveguide at a waveguide junction. The inserted SPP waves have a phase at the waveguide junction which is either a first phase or a second phase. The second phase is shifted over π with regard to the first phase and a combined SPP wave at the waveguide junction has a resulting phase wherein the dimensions of the waveguides are such that for different combinations of phases of the inserted waves the combined waves are phase aligned.